1. Field of the Invention
The invention relates to composite polymer films where the refractive index can be varied by simple compressive or extension forces.
2. Description of the Related Art
Extrusion process to produce polymeric photonic materials in the form of flexible sheets with large surface areas is known. This process gives a material comprising many thousands of alternating layers of polymers, polymer composites, and/or polymers containing inorganic or metallic nanoparticles. The polymer materials in the alternating layers can be chosen to have substantial differences in the index of refraction (n) so that the resulting materials will possess a modulation in the index with a period corresponding to the layer thickness.
Multilayer extrusion of polymers with hundreds of layers is known. The methods of fabricating dielectric reflectors and filters with specific transmission properties and pass bands are known. Properly oriented layered birefringence polymers can give multilayer mirrors that maintain reflectivity over a broad band of incident angles. Generally, the multilayer polymers have been fabricated using glassy polymers. Elastomeric multilayer with layer spacings suitable for dielectric filters and reflectors have been fabricated by sequential spin coating and by multilayer extrusion.
The fabrication of elastomeric multilayer structures with layer spacings much less than the wavelength of visible or near infrared (NIR) light has never been reported. It has not been recognized that such a composite will behave as a dynamically variable refractive index.